Solid-state imaging devices, which are widely used for video cameras and still cameras or the like, are provided in the form of a package, in which an imaging element, such as a CCD or the like, is mounted on a base made of an insulating material, with the photo-detecting region being covered by a transparent plate. In order to make the device more compact, the imaging element is mounted on the base as a bare chip. FIG. 9 shows the solid-state imaging device disclosed in JP 2001-77277, which is a conventional example of such a solid-state imaging device.
In FIG. 9, numeral 41 denotes a housing, which is made of a base 41a and frame-shaped ribs 41b formed in one piece by resin molding. An internal space 42 is formed on the upper side of the housing 41. A die pad 43 positioned at the center of the base 41a and leads 44 positioned below the ribs 41b are embedded in the housing 41. An imaging element chip 45 disposed at the center of the internal space 42 is fixed to the upper side of the die pad 43. The leads 44 include internal terminal portions 44a that are exposed to the internal space 42 at the upper side of the base 41a on the inner side of the ribs 41b and external terminal portions 44b that are exposed at the bottom side of the base 41a below the ribs 41b. The internal terminal portions 44a and the bonding pads of the imaging element chip 45 are connected by bonding wires 46 made of metal. A transparent sealing glass plate 47 is fixed to the upper surface of the ribs 41b, thus forming a package for protection of the imaging element chip 45.
This solid-state imaging device is mounted on a circuit board with the sealing glass plate 47 facing upward, as shown in FIG. 9, and the external terminal portions 44b are used to connect it to the electrodes on the circuit board. Although not shown in the drawings, a lens barrel incorporating an imaging optical system is mounted on top of the sealing glass plate 47 so that a relative position with respect to the photo-detecting region formed in the imaging element chip 45 is adjusted with a predetermined precision. During the imaging operation, object light that has passed through the imaging optical system incorporated in the lens barrel is focused on the photo-detecting region and photoelectrically converted.
Since a solid-state imaging device with such a configuration is connected at the external terminal portions 44b exposed from the bottom surface of the housing to electrodes on the circuit board, the height and the occupied surface area of the package are smaller than in configurations using a connecting structure with outer leads bent downward from the sides of the housing, thus making it suitable for high-density packaging.
In the configuration of the above-described conventional solid-state imaging device, it is necessary that the base 41a of the housing 41 has a sufficient degree of flatness. When, as conventionally, the imaging element chip 45 is fixed to the surface of the base 41a with adhesive, and the adhesive hardens, a force is caused that tends to made the imaging element chip 45 follow the surface of the base 41a. Thus, if the degree of flatness of the base 41a is not favorable, warping and internal stress are generated in the imaging element chip 45, and the electrical properties and the like of the imaging element chip 45 are adversely affected.
However, when the base 41a is molded, it is difficult to avoid a certain degree of twisting or warping of the cross-directional shape, and the degree of flatness is less than desired.